There was a kilogram of cocaine locked away in a New York City bedroom, back in 2015, and the DEA wanted to find it. So, they turned to a little known piece of technology—the Stingray.

By pinging a targeted cell phone, the Stingray mimics a cell phone tower and forces the phone to send back a signal. By calculating the strength of the signal, authorities pinpointed the location of the targeted cellphone. Once there, they found the alleged drug dealer asleep in his bed. After finally consenting to a search of his home, authorities found the narcotics, three digital scales, and empty zip lock bags.

But without a specific warrant for the search, a U.S. federal judge in New York has now suppressed the evidence. U.S. District Judge William Pauley found the defendant had a reasonable expectation of privacy within his own home, and the DEA violated his rights by using a Stingray, also known as cell site simulators, to locate his home without a warrant.

“Absent a search warrant, the government may not turn a citizen’s cell phone into a tracking device,” Pauley wrote.

In the New York case, the DEA sought a warrant to secure pen-register information (PRI) and also cell-site location information (CSLI) from the phone in question. PRI is a record of telephone numbers dialed from the specific phone. But, CSLI is only a record of geographical information derived from “pings” sent to the Stingray by the targeted cell phone. The court found that the cell phone user had a right to reasonable privacy since the user did not initiate the ping, and since cell site simulator technology is not “in general public use.”

Citing the Fourth Amendment’s protection against warrantless, or unreasonable, searches, the ruling may have effectively ended the case, and prompted a larger question: should the use of Stingrays require a warrant?

According to the ACLU, at least 24 states and the District of Columbia use Stingrays at either the local or state level, or both. However, the agency could not acquire enough information about the remaining 26 states—whether or not those state use Stingrays is unknown.

The ACLU and other privacy groups maintain that, along with the target’s phone, Stingrays also access cell information from numerous other cellphones in the search area.

According to Ars Technica, in March of this year, a Maryland court reached a similar finding, but the New York decision is believed to be a first. There are a number of states that have recently required police to obtain a warrant to use the cell site simulator technology, according to the website: California, Washington, Virginia, Minnesota and Utah.

Read the entire ruling, here